The availability of stem cell transplant as a treatment modality is dependent upon the availability of a suitable donor. Best outcomes are thought to occur in HLA matched sibling donors. The chance of a sibling being HLA matched is approximately 25%. Despite the development of large worldwide donor registries the likelihood of finding an HLA matched unrelated donor is 60-70% at best and drops to 10% in some ethnic minorities. In addition the process of identifying, confirming and harvesting an unrelated donor is cumbersome and time consuming at a time when the patient must proceed immediately to transplant (time from initiation of search to identification of an unrelated donor identification takes a median of 49 days). Therefore the development of alternative sources of hematopoietic stem cells is an area of immense interest to many investigators.